Abank sent out questionnaires to a simple random sample of customers asking whether they would like the bank to extend its hours. eighty percent of those returning the questionnaire said they would like the bank to extend its hours. of the questionnaires, were returned.

This is an example of non-response bias.

Explanation:

Non-response bias happens when potential participants of a study refuse to do so.

The bank carried out a voluntary response survey which is generally not very reliable since only those that have a strong opinion about the issue are likely to respond and participate in the survey. Those who really didn't care very much about the banking hours just didn't respond to the survey. That explains why such a high percentage of participants (80%) responded that they would like the bank to extend its working hours.

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